Why does the hydrocracking unit still experience excessive temperature rise after reaching 7 bar? How to deal with it?

Is it during the vulcanization process? Stop administering the vulcanizing agent, right? I think we should: (1) stop feeding in the vulcanizing agent, and (2) if that doesn’t work, inject nitrogen into it.

The several points you mentioned may not be based on any evidence. 1) After the bed layer started operating at 0.7 bar for self-protection, overheating occurred in the fourth bed layer when the pressure dropped to 5.0 MPa. Why is it necessary to inject a sulfiding agent? Also, is your sulfiding system always in standby mode during normal production? If not, it may take more than 10 minutes to activate the sulfiding system after overheating occurs, which could mean that the bed layer’s temperature has already risen significantly. 2) Adding fresh hydrogen to the system is absolutely incorrect; it is highly detrimental to cooling the bed layer. Let me share my personal opinion: 1. The role of pressure relief with heat retention in hydrocracking units is extremely limited. Firstly, the amount of hydrogen flowing from the compressor outlet to the reactor inlet is limited; moreover, even after heat exchange, the hydrogen still has a very high temperature when it enters the reactor, even if the reaction heating furnace has been turned off. The main purpose of pressure relief is to reduce the hydrocracking reactions, thereby minimizing heat generation (since hydrocracking is an exothermic reaction). After pressure relief, the hydrocracking reactions decrease while coking reactions increase; coking is an endothermic reaction, which is why the bed temperature drops. As a result, the catalyst activity decreases to varying degrees after each pressure relief. 2. Fourthly, the fourth bed layer you mentioned should be the lowest one. Generally, it is this bed layer that is most prone to overheating during pressure relief, as there is a phenomenon of temperature buildup. During pressure relief, if the temperature of one bed layer is high, it causes the temperature at the inlet of the next bed layer to rise, and so on, which in turn leads to a high temperature at the inlet of the fourth bed layer, resulting in overheating of that bed layer. A relatively reasonable approach is: 1) After maintaining pressure at 7 bar, release it to 0.2–0.3 MPa. 2) During the pressure relief process, it was found that the temperature at the highest point of the reactor bed exceeded the required value (usually 425°C). The 21 bar safety system was activated, and nitrogen was introduced into the system; however, the system pressure had to be lower than the pressure of the nitrogen.

The pressure should drop to 0.5 MPA when I set it at 7 bar; all the heat is carried to the fourth bed layer, so it’s normal for the temperature to be high. Once the hydrogen circulation pump starts running, the temperature will drop.

Everyone knows the procedures to follow, but the amount of N2 is very limited; it doesn’t drop to 0.5 MPa – the temperature rises once it reaches around 5 MPa, and the N2 has already been supplied. Additionally, sulfurizing agents are used to prevent the new hydrogen catalyst from being reduced. We have tried this approach twice, and it was very effective – it quickly stopped the rise in temperature. I don’t understand why everyone doesn’t agree with it; is it really necessary to follow only the methods outlined in textbooks? I think it’s difficult to innovate just by relying on textbook methods!

Regarding catalyst reduction, let me tell you that it’s not as serious as you think; there’s no need to add a sulfurizing agent. By not adding new hydrogen and using nitrogen in the bed, the bed temperature can be fully controlled. This has been used in the vast majority of hydrocracking units. If your company has an insufficient supply of nitrogen, you can consider lowering the system pressure first and then using nitrogen to create a circulation; this will help avoid the problem of hydrogen reduction of the catalyst and also serve to cool down the system. During operation, avoid the surge zone of the circulating hydrogen; additionally, when cooling down, the circulating gas should preferably flow through the cold hydrogen line as much as possible.

Could you please tell me the specific cycling process? When the cycling machine stops, does it continue to charge while discharging?

The process of handling high temperature is quite simple: first, take preventive measures, then start the hydrogen circulation pump as soon as possible. If it cannot be started, immediately activate the new hydrogen pump to supply fresh hydrogen, which will help cool down the system through the use of cold hydrogen. This should work; that’s what we do in all cases.

Personally, I think it is sufficient for the system pressure to be reduced to 5 Mpa; at this pressure, the reaction almost completely stops. This temperature increase is likely due to accumulation, and the amount of cold hydrogen supplied to the lowest two bed layers can be increased at the start of pressure relief.

Putting in new hydrogen rashly – aside from the issue of reducing CAT, could it cause a second temperature spike? :L

I’m wondering why sulfur needs to be added Even during the sulfidation process, sulfur injection should be stopped to reduce the catalyst’s activity. During the pressure reduction process, it should be reduced to the lowest possible level; if the temperature cannot be controlled, emergency nitrogen should be added, rather than hydrogen